1. Field of Invention
The present invention relates to a technique of a power line communication (PLC) modem, and more particularly, to a modem used for alternating current(AC)/direct current (DC) power line communication.
2. Description of Related Art
The home network is a necessary infrastructure construction for a digitized family, apparatuses in the future digital family will be provided with function of network connection. Power Line Communication (PLC) is one of the methods for implementing the family network. In a general power system, a voltage generated by a power plant is transmitted to a power substation through a high voltage power transmission line, and then transmitted to an outdoor transformer through a medium voltage power transmission line, so that the voltage is converted to a low voltage. The low voltage is then transmitted to each family via a low voltage power line. The PLC network utilizes such an existing hardware establishment, without additional wiring.
A PLC network can be connected with the outdoor Internet through the aforementioned medium voltage or low voltage power transmission lines, and a common user can access the network data by using the low voltage transmission line. Currently, the indoor home PLC network is a low voltage alternating current (AC) voltage (110V/220V) PLC network. FIG. 1 is a schematic view of the architecture of a PLC system. The upper portion of FIG. 1 schematically shows an indoor home PLC network. The user can access network resources through connecting the power line with a low voltage PLC modem. Such modem has a plug structure on one side, and various available digital interfaces on the other side capable of connecting to the computer, for example, Ethernet, USB, RS-232, and the like. The PLC modem can include a coupler 20, an indoor home PLC modem circuit 12, and a digital interface 14. The coupler 20 can be used to couple a signal to an AC power line 10, or to obtain data carried on the power signal from the AC power line 10 for transmission. Through the digital interface 14, the user can access data. The lower portion of the FIG. 1 schematically shows an outdoor medium voltage or low voltage PLC network, which includes a coupler 20, an outdoor network access PLC modem circuit 18, and a backbone network interface 22. This part mainly utilizes the connection between the outdoor medium voltage or low voltage PLC network and the Internet to transmit data.
FIG. 2 is a block diagram of a conventional low voltage PLC modem. FIG. 2 shows a circuit related to signal processing in the modem. The PLC used in home network is a low voltage AC PLC modem, in which the high frequency signal with information is carried onto the power line, and data is transmitted via the power line. With the conventional low voltage AC PLC modem, the high frequency signal is separated from the power line. The operation principle of the low voltage AC PLC is to transmit signals by utilizing the bandwidth ranged from 4 MHz to 21 MHz (e.g., HomePlug 1.0) or from 2 MHz to 28 MHz (e.g., HomePlug AV). The upper portion of FIG. 2 shows a receiver, and the lower portion shows a transmitter. The transmitter modulates and channel codes the user's data signals through a digital interface 44, a media access control (MAC) layer 42 and a physical (PHY) layer 40 by using an Orthogonal Frequency Division Multiplexing (OFDM) modulating technique and a Forward Error Correction (FEC) channel coding technique. The transmitter is coupled to the power line 10 through a digital to analog converter (DAC), an Analog Front End (AFE) 38 and a signal coupler and protection circuit 30, so as to transmit data. In the receiver portion, the data signal is first transmitted via a signal coupler and protection circuit 30 and the AFE/ADC 32. Then with the OFDM demodulation and FEC channel decoding 34 of the physical layer (PHY) 34, the user's data signal is demodulated and channel decoded. Subsequently, the received signal data is recovered through a MAC layer 36.
FIG. 3 is a schematic block diagram of a power processing part and a signal processing part of a conventional AC PLC modem. As shown in FIG. 3, the AC PLC modem mainly comprises two parts: one is a PLC modem signal processing part and the other is a power line AC voltage processing part. The bidirectional dashed-line flows in the lower portion of the figure shows the PLC modem signal processing part, and the unidirectional solid-line flows in the upper part shows the PLC voltage processing part. The signal processing part comprises a signal coupler and protection circuit 56, a PLC modem circuit 58 and a digital interface 60. The detail operation is the same as that of FIG. 2, which will not be redundantly described here.
The AC voltage processing part comprises an AC voltage coupler and protection circuit 50, and AC/DC converter 52 and a DC/DC converter 54. The AC voltage coupler and protection circuit 50 couples the AC voltage from the power line, and is able to suppress the surge/noise of AC/DC power and protect the AC/DC power. The AC/DC converter 52 converts the coupled AC voltages into DC voltages. The DC voltages outputted from the DC/DC converter 54 are respectively provided to the analog and the digital circuits of the PLC modem.
However, in the future, outdoor mobile platforms, such as, vehicles, transportation buses, high-speed railway, airplanes and rapid transportation systems, has gradually become a conceptual extension of a mobile office and living room in home. Therefore, it is necessary for common infrastructure constructions of both the outdoor mobile platform network and indoor home network. The outdoor mobile platform PLC network is a DC voltage (12V/24V/42V) PLC network, but the development of the current PLC technique still focuses on the AC PLC network. Moreover, since the existent AC PLC modem cannot be applied directly to the DC PLC of the future outdoor mobile platform, the current indoor network platform and the future mobile network platform are not compatible.
Therefore, it has become an urgent issue to research and develop a PLC modem that can be respectively applied in the indoor family network low voltage AC PLC and the outdoor mobile platform in-vehicle network DC PLC. In the AC/DC dual mode PLC system, the AC/DC power is the most critical part in the modem.